1. Field of the Invention
The present invention relates to electronics circuits. More particularly, the present invention relates to novel and improved method and circuit for providing interface signals between integrated circuits.
2. Description of the Related Art
Many electronics systems are implemented using multiple integrated circuits (ICs) that interface together to provide the required system functionality. In many instances, circuit interfaces are provided by digital signals having two logic levels (e.g., high and low) to express digital values. Digital signals are popular for interface because of their ease of implementation and robust immunity to noise.
Special challenges arise when interfacing a digital IC with an analog IC. Digital ICs are more efficient and cost effective for implementing digital functions such as digital signal processing and the like. Analog ICs are used to provide linear functions such as signal amplification, buffering, filtering, modulation, mixing, and so on. In many designs, the interface between the digital and analog ICs is implemented using digital signals. Within the analog IC, the digital signals are buffered, converted to analog signal(s) if necessary, and provided to the analog circuit(s).
The use of digital signals to interface digital and analog ICs is undesirable in some applications for several reasons. First, digital signals typically have large signal swing and sharp transition edges, thereby generating large switching noise. This noise can degrade the performance of the analog circuits, which typically operate on smaller signal swing. The amount of noise can be reduced, to an extent, by using separate power supplies and circuit grounds for analog and digital circuits within the analog IC. However, the reduction may not be adequate for some applications. Second, because each digital signal typically provides one bit of data, multiple (e.g., eight) digital signals are necessary to concurrently provide multiple (e.g., eight) bits of data. In addition, one or more clock signals are typically provided to latch the data bits at the receiving IC. A large number of signal lines, and a corresponding number of device pins, may thus be required to interface the ICs. Moreover, switching noise typically increases with more digital signal lines.
Accordingly, techniques for providing an improved interface between ICs using fewer signal lines that generate a reduced amount of noise are highly desirable. It is also desirable that the interface does not require complex circuitry to implement.